Low EMI emissions heat sink device

ABSTRACT

A low electromagnetic radiation emissions heat sink that dissipates heat away from an integrated circuit package by means of conduction to the electronic chassis. The heat sink may also include a ferrite ring for reducing electromagnetic radiation emissions from the integrated circuit package by increasing the electrical impedance of the EMI transmission path between the integrated circuit package and the electronic chassis, thus reducing the capacitive coupling and RFI concerns of conductive heat dissipation. The heat sink of the present invention may also include fins that are external to the electronic chassis for greater heat dissipation by means of external air convection.

CROSS REFERENCE TO RELATED APPLICATION(S)

This is a continuation of application Ser. No. 09/067,248 filed on Apr.27, 1998 now U.S. Pat. No. 6,044,899.

FIELD OF THE INVENTION

The present invention relates generally to the field of integratedcircuit heat dissipation and more particularly to heat sinks. Inparticular, this invention provides a heat sink with electro-magneticradiation interference shielding.

BACKGROUND OF THE INVENTION

It is well known in the electronic industry to provide substrate is,presumably in the form of printed circuit boards, which carry upon oneor both sides, electronic components which provide various electronicfunctions. It is also known that electronic components generate heat andcertain components also emit electromagnetic radiation which interfereswith the operation of other components on a printed circuit board orwith other electronic devices not mounted upon the board. A boardmounted electronic component may be in the form of an integrated circuitor a chip. The tendency in modern design is for integrated circuits orchips to become smaller and faster in operation. A problem which existswith faster operation of smaller circuits is that they tend to increasein temperature and may overheat to such a degree that permanent damagemay result unless steps are taken to avoid such situations.

In this case, heat removal becomes a prime necessity. However, heatremoval considerations may be contradictory to the considerationsnecessary for overcoming electromagnetic emission problems. This isbecause for the avoidance of EMI emissions, a surrounding shield isnormally necessary for an integrated circuit and this detracts from theremoval of heat because such a shield tends to act as a heat insulator.

Generally, heat sinks are mounted to an outer surface of an integratedcircuit package to facilitate the removal of heat from the integratedcircuit contained therein. Most heat sinks are thermally conductive andhave a plurality of fins to provide a large surface area, which allowsheat to be more efficiently dissipated by natural or forced air flow.Generally, heat sinks transfer heat from the integrated circuit to theair inside the computer chassis by means of convection. This increasesthe overall temperature within the computer chassis. For chips withgreater heat dissipation needs, fans are also used in conjunction withheat sinks to increase the rate of heat dissipation. Fans may bearranged to direct heat from inside the computer chassis towards holesin the computer chassis, thus moving hot air to the outside of thecomputer chassis. These fans are generally very noisy, consume power andtake-up space inside the electronic chassis.

There is a need for a heat sink device that can more efficientlydissipate heat to the outside of the computer chassis, while at the sametime reducing EMI emissions from the integrated circuit to the chassis.It would also be advantageous to be able to dissipate heat without theuse of fans.

SUMMARY OF THE INVENTION

The above and other aspects of the present invention may be accomplishedin a low EMI emissions heat sink device that dissipates heat away froman IC package by means of conduction to the top, sides and bottom of theelectronic chassis. The heat sink of the present invention may also havea ferrite ring to reduce EMI emissions from the IC package. The heatsink of the present invention may also have fins that are outside of theelectronic chassis for greater heat dissipation without the use of afan.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be better understood by reading the following moreparticular description of the invention, presented in conjunction withthe following drawings, wherein:

FIG. 1 shows a cross-sectional view of a low EMI emissions heat sinkaccording to a first embodiment of the present invention;

FIG. 2 shows a cross-sectional view of a low EMI emissions heat sinkaccording to a second embodiment of the present invention;

FIG. 3 shows a cross-sectional view of a low EMI emissions heat sinkaccording to a third embodiment of the present invention; and

FIG. 4 shows a blown-up perspective view illustrating how ferrite ringsmay be attached to a heat sink according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a cross-sectional view of a low EMI emissions heatsink 100 according to a first embodiment of the present invention. Heatsink 100 has a narrow midsection 124 and wider first and second endsections 120 and 122. End section 122 sides on top of integrated circuitpackage 110, which is plugged into socket 106. Socket 106 is mounted ona printed circuit board 112, which is mounted to electronic chassisbottom 108 by any known means. There may be a thermal compound or athermally conductive elastomer 104. Top end section 120 is locatedbetween locators 116 of the electronic chassis cover 114. The electronicchassis may be any known material, but is generally made of steel. Theheat sink 100 may be made of any known heat sink material, such asaluminum. A ferrite ring 102 is attached to the narrow midsection 124 ofheat sink 100.

Typically, heat sinks transfer heat to the air inside the chassis viaconvection. However, since the heat sink 100 of the present invention isin contact with electronic chassis cover 114, heat from the integratedcircuit package is transferred to the chassis via conduction.

This permits the air temperature inside the electronic chassis, and theresulting thermal stress on other electronic components to be lower thanthat which is typical with convective type heat sinks. The conductiontype heat dissipation also eliminates the need for a fan required inmost convective applications. This greatly improves the reliability,lowers the power consumption, and creates a virtually silent computer.Moreover, the heat sink 100 may act as a structural member, furtherstabilizing the top cover 114 of the electronic chassis, thus creating asimpler, less expensive enclosure.

The ferrite ring 102 attached to the midsection 124 of heat sink 100reduces EMI emissions to an acceptable level while still providing goodthermal performance. This is accomplished through increased electricalimpedance of the EMI transmission path between the integrated circuitpackage 110 and the electronic chassis, thus reducing the capacitivecoupling and RFI concerns that has limited previous attempts at the heatconduction approach.

FIG. 2 illustrates a cross-sectional view of a low EMI emissions heatsink 200 according to a second embodiment of the present invention. Heatsink 200 comprises a narrow midsection 203 and first and second widerend sections 210 and 212. Heat sink 200 may include heat dissipationfins 206 on at least one side. Heat sink 200 may also include a heatpipe 201 that rests on top of integrated circuit package 110 mounted insocket 106 attached to printed circuit board 112, which is attached toelectronic chassis bottom 108 by any known means. There may be athermally conductive compound or elastomer between the integratedcircuit package 110 and the heat pipe 201. There may also be a ferritering 202 wrapped around the heat pipe 201 for increasing the electricalimpedance of the EMI transmissions path between the integrated circuitpackage 110 and the electronic chassis top 114 and bottom 108. The heatsink 200 may include a tab 204, such that once the ferrite ring 202 ismounted on the heat pipe, the tab 204 is bent, and thus prevents theferrite ring 202 from sliding along the heat pipe 201.

As can be seen in FIG. 2, the first end 210 of the heat sink 200 islocated within locators 116 of the electronic chassis top 114 and thesecond end 212 is resting on the electronic chassis bottom. Accordingly,the heat sink 200 may provide structural support to the electronicchassis. Moreover, this embodiment will put less mechanical stress onthe integrated circuit package 110 than the first embodiment as thisheat sink 200 extends between the top and bottom surfaces of theelectronic chassis, rather than resting on the top surface of theintegrated circuit package 110.

Also, fins 206 may be located on a side of the heat sink that has someform of air circulation. As noted previously with the first embodiment,ferrite ring 202 provides electrical impedance of the EMI transmissionpath between the integrated circuit package 110 and the electronicchassis, thus reducing the capacitive coupling and RFI concerns thathave limited heat conduction type heat sinks in the past. As in thefirst embodiment, heat sink 200 may be any known heat sink material,such as aluminum.

FIG. 3 illustrates a cross-sectional view of a low EMI emissions heatsink 300 according to a third embodiment of the present invention. Heatsink 300 is attached to the outside of the electronic chassis along side304 of the heat sink 300 by any known means, such as screws, rivets,glue, etc. Heat pipe 301 extends through hole 310 in the electronicchassis and rests on top of integrated circuit package 110 that isplugged into socket 106 mounted on printed circuit board 112 which isattached to electronic chassis bottom 108 by any known means. There maybe a thermally conductive compound or elastomer between the integratedcircuit package 110 and the heat pipe 301.

Heat sink 300 may have fins 306 along side 304 on the outside of theelectronic chassis. This embodiment permits the heat sink 300 totransfer heat to the electronic chassis and to the external fins 306 viaconvection. The external fins permit heat dissipation by means ofexternal air movement and conduction. This is an improvement over theprior art as the heat dissipation from the integrated circuit 110 doesnot raise the internal temperature of the electronic chassis, but rathertransfers the heat to the outside of the electronic chassis.

Heat pipe 301 has a ferrite ring 302 mounted thereon, which reduces EMIemissions by increasing the electrical impedance of the EMI transmissionpath between the integrated circuit package 110 and the electronicchassis thus reducing the capacitive coupling and RFI concerns that havelimited the heat conduction approach in the past. The ferrite ring 302may be held in place by a tab 312 extending from the electronic chassistop 114. The end of tab 312 may be bent after the ferrite ring isinstalled on the heat pipe 301.

FIG. 4 illustrates a blown-up perspective view detailing how the ferriterings 102, 202 and 302 may be attached to a heat sink according to thepresent invention. Specifically, two ferrite cores 402 and 404 may beplaced around a center section 412 of a heat sink 406 and then held inplace by means of tape or a heat-shrink ring 400. Ends 408 and 410 arewrapped around the ferrite cores 402 and 404 and then secured together.This technique would be necessary for the heat sink of FIG. 1. However,the ferrite rings of FIGS. 2 and 3 may alternatively be integral ringsas they may be slid onto heat pipes 201 and 301.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andother modifications and variations may be possible in light of the aboveteachings. For example, the heat sink 100, 200 and 300 may be of anyknown heat sink material. The embodiment was chosen and described inorder to best explain the principles of the invention and its practicalapplication to thereby enable others skilled in the art to best utilizethe invention in various embodiments and various modifications as aresuited to the particular use contemplated. It is intended that theappended claims be construed to include other alternative embodiments ofthe invention except insofar as limited by the prior art.

What is claimed is:
 1. A heat sink assembly for dissipating heat from anintegrated circuit package mounted on a printed circuit board assemblywithin an electronic chassis having a top, a bottom and at least oneside wall, said heat sink assembly comprising:a heat sink having a firstend, a mid section and a second end, wherein said first end is incontact with said top of said electronic chassis and said second end isin contact with said integrated circuit package; and a ferrite ringattached to said mid section of said heat sink, such that said ferritering increases the electrical impedance of EMI transmissions from saidintegrated circuit package and said electronic chassis.
 2. The heat sinkassembly according to claim 1 wherein said ferrite ring comprises atleast two ferrite cores retained about said mid section of said heatsink by means of tape.
 3. The heat sink assembly according to claim 1wherein said ferrite ring comprises at least two ferrite cores retainedabout said mid section of said heat sink by means of a heat-shrink ring.4. The heat sink assembly of claim 1, wherein said heat sink comprises amember having a substantially I shaped cross-section.
 5. The heat sinkassembly of claim 4, wherein said heat sink comprises aluminum.
 6. Aheat sink assembly for dissipating heat from an integrated circuitmounted within within a chassis having a top, said heat sink assemblycomprising:a heat sink having an I shaped cross-section defining a firsthorizontal end portion and a second horizontal end portion connected bya vertical mid-section portion, the first horizontal end sectioncontacting the top of the chassis, the second horizontal end sectioncontacting the integrated circuit; and a ferrite ring surrounding thevertical mid-section portion of said heat sink, said ferrite ringincreasing an electrical impedance to EMI transmissions from theintegrated circuit and the chassis.
 7. A heat sink assembly fordissipating heat from an integrated circuit contained within a chassishaving a top, said heat sink assembly comprising:heat sink meanscontacting the top of the chassis and the integrated circuit forconducting heat from the integrated circuit to the top of the chassis;and ferrite ring means surrounding said heat sink means for increasingthe electrical impedance to EMI transmissions from the integratedcircuit and the chassis.